$3)$

Problem: Students in class don't know each other.

Algorithm:

$(1)$ Have each student turn to left.

$(2)$ Have student introduce themselves.

$(3)$ Have each student face forward again.

$4)$

Problem: A stack of $1000$ name tags is unsorted but should be sorted.

Algorithm:

$(1)$ Remove one tag, start a new stack.

$(2)$ Remove another tag, place in sorted order in new stack.

$(3)$ Repeat step $2$ until no tags remain in original stack.

$5)$

Problem: A stack of $1000$ name tags is unsorted but should be sorted.

Algorithm:

$(1)$ Start $26$ new stacks for names starting with A$,$ B$,...,$ Z$.$

$(2)$ Remove one tag, place in appropriate new stack, in sorted order in that stack.

$(3)$ Repeat step $2$ until no tags remain in original stack.

$(4)$ Stack the $26$ stacks into one stack in sorted order.

$6)$

Problem: Values for variables x and y should be swapped.

Algorithm:

$(1)$ Copy y$\text{'}$s value into x$.$

$(2)$ Copy x$\text{'}$s value into y$.$